Catalyzed oxidation of uranium in carbonate solutions



United States Patent 3,036,881 CATALYZED OXIDATION OF URANIUM INCARBONATE SOLUTIONS Warren E. Qliiford, San Francisco, Calif., assignor,by mesne assignments, to the United States of America as represented bythe United States Atomic Energy Commission No Drawing. Filed May 23,1957, Ser. No. 661,264 9 Claims. (Cl. 23-145) The invention relates, ingeneral, to the processing of uranium in a carbonate solution and, moreparticularly, to improved methods of catalyzing the oxidation of uraniumin a carbonate solution.

Aqueous solutions of alkaline carbonates are used extensively forleaching uranium from various solids such as ores and residues in avariety of recovery and purification processes. The carbonate solutionsare alkaline and contain variable ratios of carbonate and bicarbonateions dependent on operating pH conditions. In such a solution hexavalenturanium is complexed by the carbonate ion to form uranyl tricarbonateion, UO (OO as the soluble species; however, at least a part of theuranium in such ores and residues often occurs in a lower valentoxidation state which does not readily produce a species 'which issoluble in such leach solutions. Also, the uranium may be partiallyreduced by contact with steel processing equipment or other etfectivereducing agent during mining or preliminary processing.

For example, if a uranium mineral such as pitchblende, uraninite orcofiinite is present in the ore the carbonate leach solution does noteifectively dissolve all of the available uranium since the lower valentstates, especially the tetravalent, does not dissolve in the solution orreact to produce insoluble hydrous oxides or hydroxides on contact withthe ore. Under other process conditions in which the leach solutioncontains an excess of CO and the OH is buffered out with H003, a solubletetravalent uranium carbonate may be produced; however, this complex isvery unstable if the OH concentration increases during processing anduranium can be lost from the solution by precipitation as U(OH) at anin-,

appropriate time in the procedure. In conventional practice, uraniumores may be oxidized by roasting 'in This procedure is not alwayseffective, entails additional operations and equipment, and cannot beapplied to solutions. Chemical oxidation may be slow and reagent costhigh.

The present invention is predicated on the discovery 7 that certainmetallic ions catalyze the oxidation of lower valent states of uraniumin such a solution with the oxygen in air, 0 and also by hypochlorite.Such catalysis is made more effective by the provision of superioroperating conditions and combinations of reagents in oxidizing uraniumcontained in carbonate solutions in general, and is equally effective inoxidizing uranium presa ent in solid materials during leachingoperations thereby preventing the formation of insoluble lower valenthydroxides in such solutions and speeding up as well as increasing theamount of uranium leached thereby. Subsequently, the carbonate solutionmay be processed for 6 the recovery of uranium by various proceduresincluding processes as conventionally practiced, e.g., in the domesticmining industry.

Accordingly, it is an object of the invention to provide a catalyticprocess for promoting the oxidation of lower valent uranium compounds inan alkaline carbonate solution.

Another object of the invention is to provide a catalyzed air oxidationmethod for use in the carbonate leaching of uranium containing solids toimprove the recovery of uranium therefrom.

aasassi Patented May 29, 1962 Still another object of the invention isto provide a catalytic method for promoting the oxidation of uranium ina carbonate solution with air, oxygen gas, and hypochlorite oxidizingagents.

One other object of the invention is to provide a carbonate leachingprocess employing hypochlorite oxidizing agent for the more economicalleaching of lower valent uranium compounds and minerals from solids.

A further object of the invention is to provide catalyzing agents forpromoting the oxidation of lower valent uranium ionic species and/oruranium compounds in a carbonate solution.

A still further object of the invention is to provide 8. catalyzedoxidation carbonate leaching process for improving the recovery ofuranium from ores containing uranium in lower valent oxidation states.

Other objects and advantages of the invention will become apparent byconsideration of the following description.

The starting material in the present process may comprise uranium oxidessuch as U 0 U0 lower valent hydroxides such as U(OH) orprimary-secondary uranium minerals such as carnitite-uraninite ores, allof which may contain uranium in oxidation states lower than thehexavalent and particularly the uranous and mixed uranous-uranyl states.Residues obtained in other processes and having generally similarcharacteristics may likewise be processed. Solutions or other materialscontaining lower valent uranium compounds can likewise be converted tothe carbonate form and the oxidative process of the invention appliedthereto. The ore materials or other solid, if necessary, are firstsubjected to grinding and screening to provide the proper particle sizeto render the uranium content accessible to the leaching solution.'Customarily, particle sizes in the vicinity of minus mesh are adequate;however, with certain ores, e.g., limestones, grinding to nominallyminus 325 mesh may be required. Solutions are converted to the carbonateform by adding Na CO or NaHCO thereto.

In accordance with the invention, the iinely divided source material isdisposed in equipment adapted for heating, agitation, and theintroduction of reagent solutions and gases if air or 0 is to beemployed as the oxidant. The solid is then contacted at elevatedtemperatures with an aqueous alkaline carbonate solution under catalyzedoxidizing conditions to selectively leach uranium therefrom. In theevent that vanadium is present some vanadium is also leached; however,most other materials which are present in ores and residues are notleached to any great extent.

More particularly, carbonate solutions containing from about 4 to 10% ofsodium carbonate and/or from about 0.25 to 7% of sodium bicarbonate aregenerally used. Certain very favorable ratios and regent concentrationlimits of the reagents and concurrent pH conditions will be set forthhereinafter.

For the purposes of the invention catalytic quantities of compounds ofcertain metallic elements are added to the solution to provide ionicoxidation states of the metals which effectively promote the oxidationof the uranium in the solution. In theory the ions of anyoxidation-reduction couple above OH -air and UO UO (CO could act as acatalyst; however, it is found experimentally that some substancesmeeting that qualiappropriate compounds to carbonate solutions arecatalytically active in oxidation with or air: C+ +--Co+++; V+ V+Tl+-Tl+ and Mn+ Mn+ or possibly Mn+ --Mn+ on consideration of theoxidation potentials. The ions of the couple Cu+--Cu++ are veryeifective for the indicated purpose. Moreover, the catalytic eifect ofthe Cu species is greatly enhanced on addition of ammonia to the systemand the Cu catalysis is also effective when using hypochlorite (or C1 asthe oxidant. Consideration of the various couples indicates thatsuitable couples require, as a minimum, that the oxidation potential beabove the OH--air couple and about equal to or greater than the H O HOcouple consistent with the view that oxygen reduction which isconcurrent with uranium oxidation proceeds stepwise through peroxide.The potentials of the foregoing couples are disclosed, for example, inchapter IV,, under Oxygen of The Oxidation States of the Elements andTheir Potentials in Aqueous Solutions, by Wendell M. Latimer, publishedby Prentice-Hall, Inc., 1938. The above-indicated catalytic species areproduced on the addition. of compounds such as KMnO MnO MnSO CuSO Cu O,CuCl ,TlNO and V 0 in amounts ranging from 0.1 mg./liter for the moreeffective catalysts such as the copper couple to a few grams/ liter ofthe less efiective materials as discussed further hereinafter.

'In practice, leaching is conducted at temperatures solutions byreducing agents such as Na S O' Zn and ammonia, and Zn and cyanide.Treatment with 0.2% sodium amalgams finely dispersed in solutions atabout 25 C. also precipitates the uranium as a hydrous oxide.

Necessary conditions and procedures for obtaining beneficial results inaccordance with the teachings of the invention will be apparent from thefollowing description of systematic experimental studies of variousoperating conditions.

At the outset, the distinctive behavior of various additive agents withreference to oxidative leaching was explored using a standard procedure.wherein various amounts of the agent were added to a leach solutioncontaining 0.5M Na co and 0.5M NaHCO in contact with 5 g./liter of U 0at a temperature of 90 C., with air blown at a standard ratetherethrough and for a standard time period. A number of control runswith no additive were made to serve as standard, giving a range of 20 toof the U 0 being dissolved. From the results, tabulated below, thematerials can be classed as inhibitors, as having no effect, as beingoxidants, or as being catalysts. The difierentiation between the latteris made on the basis that catalytic agents improve the leaching wheneither the oxidized or reduced form of the agent is introduced, whileoxidants improve the leaching onlywhen the oxidized form is addedgenerally in much larger amounts than is required for catalysis.

TABLE I Agent (Inhibitors) Percent Agent (No Effect) Percent LeachedLeeched 25 g./1 FeSO4 1 5 g./l. Na indigodisulionate 20 25 g./l.Pyrogallolmfl 1 5 gJl. Na diphenylamine p-sul 25 g,/l. NH1OH-HCL 3ionate 20 5 g./1. Quinhydrone-.. 6 5 g./l. Na 1-10 phenanthroline 5g./l, SnClz-ZHzO 5 monohydrate. 20 25 30 30 25 15 20 Agent (oxidants)Percent Agent (Catalyst) Percent Leeched Leeched 100 30 5 g./l. v 5g./l. P 20 5 g. 5 ELI]. 100 5 g./l. 011504515120 100 5 g /l. 25 8.5 gJl.OHSOASHZO +NH4OH 100 5 gJl. 50 5 all. C1120 70, 5 g./1. 100, 5 g./l.CoO1z-6Hq0 55 5 g./l. 5 g./l. OOOln-GH; +NH OH 45 5 g./l. 100 5 g./l.TIN 45 5 gJl. Hg 20 5 g.[l. 60 8 g./l. NaC10(Purex) 85 Followingleaching, the uranium is separated from the leach solution by a varietyof conventional filtration or centrifugation processes. The uranium canbe'precipitated from leach solutions containing vanadium as a syntheticcarnotite by acidification to a pH of about I A standard procedure andexperimental apparatus was employed for a more complete elucidation ofthe operating conditionsusing U 0 U0 .ulraninite and other ores. 300m1., of leach solution. was disposed in a 500 7 ml. 3-neck'flask and thesystem purged with the test gas 6 from which the uranium and vanadiumcan be obtained a. V

as U0 and V 0 by standard processes. The uranium can also be recoveredand purified from such solutions by adsorption on a strong base anionexchange resin such as Dowex 1 followed by selective elution as.disclosed in the copending application of Richard H. Bailes et -a1.,Serial No. 362,122, filed June 16, 1953, which issued as Patent No.2,864,667 on December 16 1958. Uranium is also precipitated from suchcarbonate leach" (air, 0 or N and a bubbling flow of about. 10 mL/min.of the gas was continued during the experiment with ,Oontmuous stirring.I Thetemperature was brought to the desired level and solid containinguranium equivalent to 1 g./liter of solution was added. Copper and othercatalysts were added as solids-or solutions, e.g., CuSO solutions.Samples were taken hourly and uranium determined fiuorinietrically.

A stock quantity of U O 'was prepared by the decompositionof U0(Shattuck) at'1100' C. yielding a that given in ASTM 'data card No.4-0518. The U0 material whose X'-ray diffraction pattern agreed with Wasalso obtainedfrorn S. W. Shattuck Co., lot No. 10054:and yielded'X-rayzdifr'raction data typical of prepared UO j ;Uraninite labeled'Urananite (Pitc'hblende) from theGreat Bear Lake area and analyzing 50%U 0 was obtained from Wards. The ores, all ground to l00 mesh, tabulatedbelow were also used. It is to be expected that lots of difierentorigins and different methods of preparation will vary in behavior;however, results with identical lots will be self-consistent andaccurately indicate consistent trends in the several variations of theprocess described hereinafter.

EFFECT OF SOLID CONTENT IN SOLUTION The effect of variations in theamount of solid source material present in the solution was determinedusing mg./liter of Cu added as CuSO at 90 C. air bubbled yielding themaximum leaching rates with the leaching solutions as tabulated below:

TABLE Fraction U 0 leached per hour Conditions 1 g./1. max. 2 g./1. max.

.5M NazCOz-.5M NaHCOa 0.14 0. 15 .'5M NazOO .5 NaHCO3, .lM NH OHH 0.0.31 .9M NlzC 03.1M NaHCOa 0. 23 0. 24

As anticipated the initial leaching rate, i.e., the max. rate, isdirectly proportional to solid content within experimental error;however, since the relative rate of leaching was essentially independentof the solid content the remainder of the experiments were done usingsolid equivalent to 1 g./l. of U 0 That the absolute rate of leachingdoes not fall off as rapidly as might be expected may be due to the factthat surface area (to which the rate should be proportional) does notdecrease as rapidly as the volume (to which the weight is proportional).The large increase in extraction rate using ammonia is apparent therein.

TEMPERATURE EFFECT 0.5M Na CO 0.5M Natl-I00 solutions catalyzed with Cu(CuSO with and without ammonia were used to leach U 0 at 70 and 90 C.with air bubbling and with the results tabulated below:

The results indicate that leaching at temperatures as V low as 70 C. areuneconomical and that leaching at 90 C. is much more preferable so thatthe remainder of the experiments were done at 90 C. At temperaturesabove 80 C. the leaching rate increases at a rapid rate.

EFFECT OF IONIC STRENGTH Since pH changes in a CO =-HCO system result inlarge changes in ionic strength, controlled leach solution pairs in oneof the members of which was included 6 substantial amounts of sodiumsalts were used to leach U 0 at C. air bubbling with other conditionsand results tabulated below:

TABLE V Fraction U305 Conditions leached per hour .5M Na2CO .5M NaHCO3,25 mg./1. Cu 0.14 .5M NazCO .5M NaHCO 25 mg./1. Cu, AM Na1SO4 0.14 .9MNa2CO -.1M NaHOO; 0.035 .9M NtizCOr-JMI NaHCOa, .41 NaNO; 0. 040

As may be seen therefrom, variations in ionic strength have little, ifany, eifect on leaching rates.

EFFECT OF COPPER CATALYST CONCENTRATION Leach rate variations withvarious copper catalyst concentrations, added as CuSO solution, weredetermined using two different leach solution compositions, with bothair and N bubbling at 90 C. to leach U 0 with the results tabulatedbelow:

TABLE VI Fraction UaOs Leeched Per Hour Air Air It will be seen from theforegoing that the leach rate increased with increasing Cu catalystconcentration in all cases although the power dependence is considerablyless than one. The remarkable effectiveness of the catalysis on airoxidation with even very small amounts of Cu is apparent. Under N thedependence on Cu appears to be approaching the first power at low Cu concentrations. Under air the dependence is much less even correcting fordirect air oxidation which might be occurring simultaneously. Note thatat 25 mg./l. On the rate under N is much lower than under air even whenthe latter is corrected for air oxidation. This observation can only .beexplained by the formation of oxidizing species other than cupric in theair blown system. The obvious explanation is the formation of peroxidein the reoxidation of cuprous ion or copper metal if, during thecatalytic reaction, the cupric state is reduced to that extent.

Various mechanisms are possible to explain the results although simplemechanisms alone cannot explain the data, i.e., that the rate under air(corrected for meatalyzed direct air oxidation) is times that under Ninstead of twice or four times which may be explained by simplemechanisms.

EFFECT OF INCREASED O2 CONCENTRATION U 0 was leached under standardconditions described above at 90 (3.; however, 0 was bubbled through theleach solution of the character and with the results tabulated below.The results of comparable operations with air are included forcomparison.

TABLE VII Fraction U303 Leached Conditions Per Hour Air 02 .5MNazCOa-.5M N aHCOa 0.01 0.04 .5M Na CO -5M NaHCOa, 2.5 mgjl. Cu, 0.110.12. .5M N22C0$.5M NaHCOg, 2.5 mgJl. Cu+.1M

NH4OH 0.165 0. 17 .9M NazC03-.1l\/I NHHCOx, 2.5 mgJl. Cu 0.19 0.23

TABLE VIII r Fraction Conditions U303 Leached Per Hour .5M NagCOs-JSMNaHCOg, 25 mgJl. Cu 0.14 .25M NazCOa-.25M NaHCOa, 25 mg/l. Cu 0.14 .9MNarCO .1M NaHOOS, 25 mg./l. Cu.-. 0.23 .45M Na2CO3--.05M NaHCOg, 25mgJl. Cu 0.16

-It will be noted that a CO =/=HCO ratio of 1, the indicated change intotal carbonate species concentration produced no change in the leachingrate. At a ratio of 9, the rate fell 0E considerably indicating that theleaching rate is critically and increasingly dependent on the HCOconcentration in the range of 0.05M to 0.1M than it is in the range of0.25M to 0.5M. Also, the rate at 0.45M OO =0.05M HCO is higher than at0.5M CO =-0.5-M HCO even though the total concentration of carbonatespecies as well as HCO is lower. These facts indicate that thevariations noted are attrib utable to pH variations and not to ionicstrength or total carbonate concentrations, a deduction which isconfirmed hereinafter.

EFFECT OF VARYING pH Pairs of solutions with varying amounts of @801catalyst with ratios of 1:1 and 9:1 of CO =/HCO were used to leach U 0at 90 C. in air and N with the results tabulated below: a

from 1 to 9 increased the rate. of leaching in all cases. When the ratiowas changed to 0.11 the leachingrate was lower. The leaching rateratios. under 'air are re- 8 mainingconstant, CO concentration and pHare interrelated. The change in ratio of 0.5M Na CO -0.5M H00 to 0.9M NaCO -0.1M'NaHCO corresponds to a pH change from 9.9 to 10.9 or afactor of10 in OH- concentration. The benefits'to be derived from operating withCO =/-HCO ratios givinga'pI-I near 10.9, i.e., a practical range ofabout pH 10.5 to 1121 being indicated, are obvious.

CATALYTIC ENHANCEMENT VITH COMPLEXING AGENTS Leaching solutions ofconstant 0.5M NagCO --0.5M NaHCO composition with various complexingagents present were used to leach U 0 at 90 C. with air bubbling withthe results tabulated below:

It will be observed thatammonia greatly increased the rate whilepyridine and ethylenediamine have a slight beneficial efiect. Cyanidehad a strong adverse eifect explainable by the fact that CN- complexesthe cuprous state so strongly that reoxidation cannot take place and thecatalytic cycle is blocked. The ammonia undoubtedly converts the copperto a more efiectiveionic species having different charge characteristicsand more favorable oxidation-reduction potentials than those present inthe absence of ammonia.

COPPER-AMMONIUM CATALYSIS VARIABLES (1) Concentration of catalyst: Pairsof 0.5M Na CO -0.5M NaHCO solutions containing diiferent amounts ofCu(CuSO with and without ammonia added were used to leach U O -at 90 C.and with air bubbling, with the results tabulated below:

TABLE. XI

Fraction U 05 Leached Per Hour .5M NaHCOa Ratio As may be noted the rateof leaching increases much more rapidly with increasing Cu(NHconcentration than'with Cu. (ionic species) alone, though the dependenceis still less than'first power. .The enhancement effect of ammonia. maybe quite specific for copper since in similar e'irperimentswith Co and0.1M NH OH the rate was only 0.021 as compared to 0.020 for no markablyconstant indicating the complete elfectiveness of even very smallamounts of Cu catalystunder the indicated conditions. With totalcarbonatespecies re catalyst as above. r

(2) NH OH'concentration'eflects: Solutions containing 0.5M Na CO 0.5MNaHCO and equivalent amounts of Cu (25 mg.) w.ere used to leach U 0 atC. with air bubbling withthe'results tabulated below:

' r TABLE XII 1 r Fraction U308 Conditions Leached Per V Hourintimation;..;.l. 0.29 ,25M NH1OH .5 0. 29

It will be observed that increasing the ammonia concentration from 0.1Mto 0.25M had no effect. The possibility that the catalytic couple isVarious ores were leached for 6 hours at 90 C. with air bubbling withthe results tabulated below. Control runs using a standard oxidant areincluded for comparison.

is therefore doubtful since the ammonia concentration would effect thepotential of such couple thereby aifecting the leaching rate. Thiscircumstance may indicate that the catalytic couple involves a mixedammonia-carbonate complex, e.g., Cu(NH +Cu(NI-I CO It is apparent thatammonia concentrations lower than 0.1M should also be effective, e.g.,0.025 or 0.050 and above.

CATALYTIC LEACHING OF OTHER SOLIDS Carbonate solutions were used undercontrol and various catalyzed conditions to leach U0 uraninite andvarious ores at 90 C. with either air or 0 bubbling and with the resultstabulated below:

TABLE XIII U0 Leaching Results The improved results were similar tothose obtained with U 0 i.e., Cu catalysis improved leaching and theimproved leaching is enhanced at higher pH and in the presence ofammonia. yielded a more pronounced enhancement in the present case thanwith U 0 supra.

Uraninite was leached similarly to the U0 above with Moreover, the useof 0 also As may be noted the copper-ammonia catalyzed aerated leachingis at least as good if not superior to any other tested. The resultswith the indicated ores would be further improved with finer grinding inaccordance with conventional practice.

HYPOCHLORITE OXIDATION AND LEACHIN G While copper catalyzed aerationoxidation leaching, especially with ammonia, is very economical and atleast as good as any other, the required equipment may sometimes be morecomplex and engineering costs are somewhat greater than using standardchemical oxidants. Permanganate has generally been found most elfectivein conventional practice. However, it has now been found thathypochlorite oxidation is quite rapid and efficient and, moreover, isalso improved by copper catalysis. The equivalent reagent cost ofhypochlorite is less than with permanganate. For example, a 25% excessof hypochlorite over the stoichiometric amounts required to oxidize0.0037M U0 gave 100% leaching with a carbonate leach solution in 6 hoursat 90 C. Variables in hypochlorite leaching were studies as follows:

HYPO CHLORITE CONCENTRATION The effect produced by varying thehypochlorite concentration was determined by leaching U0 solid with 0.5MNa CO 0.5M NaI-ICO solutions at 90 C. N atmosphere with aqueoushypochlorite added in the amounts and with the results tabulated below.The N atmosphere is employed to eliminate air oxidation effects whichwould complicate interpretation of results. In actual practice airatmosphere could be used thereby obtaining enhanced results andadditional economics.

the following results: TABLE I i TABLE XIV 0 GT Fraction U0, UraniniteLeaching Results on 1 Ions EES Fractions .Uraninite Leached 16.7m1./1.5% N aCl0r 0, 83 Per Hour 6.7 m1./1.5% NaClO 0. 46 ConditionsFlrstfiw Last 40% As may be noted the rate of leaching increases with h.0 20 0 085 increased ClO- but with a low power dependence (beg g ffjf'gfiiij::::::::"I: 0:087 tween 0.5 and 1.0). The lower apparent rate maybe 5 J C N 4 0-105 due to disproportionation of C10 into Cl and C1O"effect appears to'be most pronounced during dissolution of the initial60% of the uranium.

solutions and the solutions were employed to leach U0 11 solid at 70 and90 C. in N with the results tabulated below:

TABLE XVII Fraction U09 Conditions, C. Leached Per Hour As in airoxidation lowering the temperature decreases the leaching ratesignificantly and it is therefore preferred to operate in the range of80 C. to above 90 C.

CATALYSIS Various possible catalytic agents were added to 0.5M

Na CO -0.5M NaI-ICO' solutions with 6.7 ml. of NaClO present whichsolutions were used to leach U0 at 90 C. N atmosphere with the resultstabulated below:

As above Cu(CuSO exerts a pronounced catalytic effeet. The fact thatcupric materials should exert about the same absolute effect as in airis reasonable since the reoxidation of the reduced copper species is notthe slow step in the catalytic cycle, hence the character of the oxidantmakes little difference.

EFFECT OF pH VARIATION Leach solutions of varying carbonate speciescontent and containing 6.7 ml. of 5% NaOlO were used to leach U0 at 90C. and with an N atmosphere with the results tabulated below:

TABLE XIX Fraction U01 Conditions Leached Per Hour 1M NaHCO;1(i.e.:l:.75) .5M NaHCO -.5M NazC0 0.46

EFFECT OF HYPOCHLORITE CONCENTRATION (UaOs) The eifect of varying ClO"concentration on the leaching of U from U 0 was studied by adding twodiiie'rnt amounts of 5% NaClO to 0.5M Na CO 0.5M NaHCO 12 sults with thesame lot of U 0 and U0 for which no explanation is apparent.

EFFECT OF pH ON HYPOCHLORI'IE LEACHING (U305) U 0 was leached with 1Mtotal carbonate species concentration at different pH values with acarbonate leach solution containing 6.7 ml. of 5% NaClO at 90 C. in N;as with U0 with the results tabulated below:

TABLE XPG Fraction UaOs Conditions Leaehed Per Hour 1M NaHCO 0.45 .5MNaHC0 .5M N81200:; 0. 32

Note that the rate in 1M NaI-ICO is substantially greater than with 0.5MNa CO -'0.5M NaHOO' and similar reasoning is applicable as with U0 OVRELEACHING WITH HYPOCHLORITE Various carbonate solutions with 6.7 ml.NaOlO were used to leach various ores for 6 hours at 90 C. with airblowing (oxidation) with the results tabulated below:

TABLE XXII Percent U 03 Leeched Ore 1M HCOr .5M CO .QM CO .5M H00 .lMH00 Monticello N0. 27 81 Big Buck No. 10521... 47 58 ACM Grey Special 93Garwood & Gerlock No.

Under the observed conditions, the pH dependence noted above apparentlydoes not apply; however, the results are explainable on the basis thatair-oxidation leaching increases with increasing pH and that this efiectis dominant. in any event it can be seen that leaching as above iscomparable to that achieved with 0.600 g./l. of KMnO or copper-ammoniacatalyzed air oxidation leaching. The amount of hypochlorite is cheaperas chlorine than the amount of KMILOL; required to obtain equivalentrecovery. Moreover, a far less objectionable contaminant solution incontact with U 0 at 90 C. in an N atrnos phere under the conditions andwith the results tabulated It is interesting to note that the leachingrate with;

U 0 is less than with U0 with the same NaClO concentration. This is thereverse of the air oxidation reis introduced into the system. 7 7

While there have been described in the foregoing what may be consideredto be preferred embodiments of the invention, modifications may be madetherein without departing from the teachings of the invention and it isintended to cover all such as fall within the scope of the appendedclaims. j

What is claimed is:

1. In a process for leaching uranium from a solid containing uranium inhexavalent and lower oxidation states, the steps comprising contactingsaid solid with a carbonate leach solution containing catalytic amountsof the ionic species of copper in the presence of'aminonia at atemperature of above about C., and simultaneously add- "ing an oxidizingagent to said solution to oxidize and ,dissolve the uranium" from saidsolid. 7 7

L 2. A process for recovering uranium from a solid containing uranium inhexavalent and lower valent states comprising reducing said solid to aparticle size of below about mesh, contacting said solid with acarbonate ,leach solution containing ammonia together with catalyticamounts of ionic species of copper at a temperature of above about 80C., simultaneouslyadding an oxidizing agent to said solutionto oxidizeand, leach the uranium fronfsaid solid to produce a carbonate leachsolution containing hexavalent uranium, and recovering uranium from theleach solution. i j

3. 'A process for recovering uranium from a solid containing uranium inhexavalent and lower 'valent states comprising reducing said solid to aparticle size of below about -100 mesh, contacting said solid with acarbonate leach solution containing catalytic amounts of ionic speciesof copper in the presence of ammonia at a temperature of above about 80C., simultaneously adding at least one oxidizing agent selected from thegroup consisting of air, and hypochlorite to said solution, saidcarbonate solution having a ratio of CO =/HCO concentrations yielding apH in the range 10.5 to 11.1 with said air and O oxidants and a HCOconcentration of about 1M with said hypochlorite oxidant to oxidize andleach the uranium from said solid to produce a carbonate leach solutioncontaining hexavalent uranium, and recovering uranium from the leachsolution.

4. The process as described in claim 3 wherein said oxidizing agentcomprises air.

5. The process as described in claim 3 wherein said oxidizing agentcomprises air and said temperature is about 90 C.

6. The process as defined in claim 3 wherein said oxidizing agentcomprises 0 7. The process as defined in claim 3 wherein said oxidizingagent comprises hypochlorite.

8. A process for recovering uranium from a solid containing uranium inhexavalent and lower valent states comprising reducing said solid to aparticle size of below about -10!) mesh, contacting said solid with acarbonate leach solution having a pH in the range of about 10.5 to 11.1,containing ammonia together with catalytic amounts of ionic species ofcopper at a temperature of above about 0., simultaneously providing anoxidizing agent in said solution to oxidize and leach the uranium fromsaid solid to produce a carbonate leach solution containing hexavalenturanium, and recovering uranium from the leach solution.

9. The process as defined in claim 8 wherein said carbonate leachsolution is at a temperature of about C.

References Cited in the file of this patent UNITED STATES PATENTSThunaes et al Nov."12, 1957 OTHER REFERENCES

1. IN A PROCESS FOR LEACHING URANIUM FROM A SOLID CONTAINING URANIUM INHEXAVALENT AND LOWER OXIDATION STATES, THE STEPS COMPRISING CONTACTINGSAID SOLID WITH A CARBONATE LEACH SOLUTION CONTAINING CATALYTIC AMOUNTSOF THE IONIC SPECIES OF COPPER IN THE PRESENCE OF AMMONIA AT ATEMPERATURE OF ABOVE ABOUT 80*C., AND SIMULTANEOUSLY ADDING AN OXIDIZINGAGENT TO SAID SOLUTION TO OXIDIZE AND DISSOLVE THE URANIUM FROM SAIDSOLID.